| Under the background of rapid urbanization,the increase of impervious surfaces area(ISA)is an important factor affecting the deterioration of the ecological environment in urban agglomerations.The changes in the spatial structure of the ISA have changed the distribution of surface heat and exacerbated the problems of large-scale land surface thermal environments in the urban agglomerations.The Guangdong-Hong Kong-Macao Greater Bay Area(GBA)is one of the fastest urbanizing urban agglomerations in China.Therefore,this study aimed to investigate the impact of the spatial-temporal changes of the ISA structure on the land surface thermal environment in the GBA.This study has important theoretical and practical significance for the sustainable development of urban agglomerations.This study was based on the Landsat remote sensing images and MODIS data to extract ISA information and land surface temperature(LST)information from 2000to2015.The various geospatial methods were used to analyze the spatiotemporal dynamics of the ISA spatial structure,including the analysis of the ISA expansion pattern and direction base on the buffer zones method,the analysis of the internal density change of the ISA with the density gradient method,and the landscape-based metrics statistics to analyze the variability characteristics of ISA landscape patches.In addition,the mean-standard deviation method is used to classify the LST to analyze the spatial-temporal evolution of the land surface thermal environment of urban agglomerations.Finally,the influence of the spatial structure of the ISA on the land surface thermal environment is analyzed through spatial analysis and correlation analysis.The main contents and conclusions are as follows:(1)The results indicated that the ISA in the GBA drastically expanded from1169.293 km~2 in 2000 to 9754.936 km~2 in 2015.The main expansion pattern are“external radiation”expansion from the center of the study area to the surrounding area,“band-like”expansion along the main transport route of the bay and the"filled"expansion.Among them,the expansion pattern of the ISA is different in stages.The first growth peak was from 2000 to 2005.The urban expansion pattern was rapid outward radiation expansion;The second growth peak was from 2005 to 2015,and the urban expansion pattern was transformed to urban infill.The main expansion directions were east,southeast and south.The proportion of ISA within 15 km buffer zone from the center of the study area in each year is the largest.(2)The internal density of ISA in the GBA increased significantly from 2000 to2015.The ISA density was distributed from high to low from the center of the urban agglomeration to the fringe area.The area of ISA in the low density area dwindle down and the has the largest proportion.While the areas of ISA has been increasing each year in the sub-medium density area,medium density area,sub-high density area and high density area.And the high density area are mainly concentrated in the central area of GBA and coastal traffic corridors.In addition,the change in the landscape-level metrics of the ISA reflected the ISA patches were continuous increased,gradually fragmented,shape complicated and aggregation was reduced.From the change of the class-level metrics,we find that there are less patches in the high density area with larger patches per unit area,simpler in shape,more aggregated and connected and less fragmented than compared to low density areas.This trend is rising year by year.(3)The LST(daytime and nighttime)of GBA was exhibiting a significant‘upward trend'from 2000 to 2015.The mean LST increased by 7.41°C and 10.23°C in the daytime and nighttime respectively.The central area of the urban agglomeration are high temperature zones had gradually expanded year by year.The LST decreases with increasing distance from the urban agglomeration center.With each 15 km increased in the distance to the center,the LST decreased by 0.15°C.The15 km buffer zone closest to study area's center had the highest the mean LST(daytime and nighttime)for all years.(4)As the ISA of the GBA expansion outwards,the area of high temperature zones continued to expand from 2000 to 2015.They have high spatial consistency.The thermal properties of the underlying surfaces of urban agglomerationsthat change due to different urban expansion patterns of the ISA are the leading factors that cause the LST to rise.In addition,the internal density of ISA has increased significantly in the GBA in the past 15 years,especially in the central area of the urban agglomeration.The density of the ISA had a significant positive correlation with the mean LST along the density gradients in the all years both in daytime and nighttime.The LST(day and night)of each density area increased year by year,and the temperature difference between neighboring grades decreases year by year.The changes of the LST(daytime and nighttime)had been more pronounced in the high ISA density areas for all years,the mean LST of the high density area of the ISA is about 2.85°C higher than that of the low density area.The landscape-level metrics and class-level metrics are significantly correlated with LST.This provide evidence of the impact of the internal landscape composition and patterns of ISA on the LST variability in the GBA.The results highlight the important role of the ISA high density areas in increasing the impact of the LST.The ISAs with larger patches in the high density area that are simpler in shape,more aggregated and connected,and less fragmented seem to exacerbate elevate in the LST.In general,the center of the urban agglomeration is the place with the highest ISA density,which rise the LST in the continuous area and radiates around,and thus affecting the regional thermal environment of GBA.(5)In particular,the nighttime LST were affected by the environmental characteristics of urban agglomeration.Especially the study area is adjacent to the oceans and there are a lot of paddy fields.The correlation between the LST and the spatial structure of the ISA was higher at daytime than at nighttime. |
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